The present invention relates to a rotary electric machine for mounting on a turbine generator and the like.
A rotary electric machine has a cylindrical rotor with slots formed in its circumference at equal intervals, as shown in FIG. 1 to FIG. 3 (details will be described later). Inserted in each of the slots are a field winding, a creepage block for insulating the field winding, and a wedge for preventing the field winding from coming off.
When, upon energization of the field winding, the rotor incorporating the creepage block rotates at high speed, the field winding is subjected to heat produced by electric current flowing therein and a high surface pressure from the creepage block and wedge produced by a large centrifugal force of rotation and is therefore thermally elongated.
At this time, the most radially outward turn of the field winding slips relative to the creepage block. If a friction coefficient between the creepage block and the field winding is larger than that between the creepage block and the wedge, a slippage occurs between the creepage block and the wedge.
Further, when the friction coefficient between the creepage block and the wedge is larger than that between a wedge side surface and a tooth side surface, the slippage shifts to between the wedge side surface and the tooth side surface.
When these friction coefficient values vary from one slot to another in the rotor, a bending force acting on the shaft of the rotor also varies, resulting in a bending of the rotor shaft.
This bending will ultimately lead to an abnormal shaft vibration of the rotary electric machine and thus must be minimized. Even if all the slots have identical friction coefficient variations but if the slipping portion varies among the contact between the field winding and the creepage block, the contact between the creepage block and the wedge, and the contact between the wedge and the rotor shaft, a moment arm on the rotor shaft will ultimately change, resulting in the shaft being bent.
Means for addressing the problem of the rotor shaft bending described above are disclosed in, for example, JP-6-86492A, JP-7-163075A and JP-8-322180A.
In the examples disclosed in JP-6-86492A, a sheet, which is made of graphite and covered with polytetrafluoroethylene, is interposed between the most radially external turn of the field winding and the next most external turn to improve the slippage between the adjoining turns of the field winding.
The example disclosed in JP-7-163075A comprises a field winding received in each coil slot, a wedge inserted into an opening of the slot to firmly hold the field winding in the slot, and a low-friction coefficient material, such as aramid paper, coated with polytetrafluoroethylene and interposed between the wedge and the field winding to improve the slippage of the field winding.
Further, in the example disclosed in JP-8-322180A, a low-friction coefficient material, such as polytetrafluoroethylene, is integrally formed between the wedge and the field winding in the rotary slot to improve the slippage of the filed winding.
The conventional techniques described above have the following problems.
All the prior arts of JP-6-86492A, JP-7-163075A and JP-8-322180A are the examples of attempting to reduce a frictional force acting on the field winding and therefore the shaft bending force by inserting a member coated with a friction coefficient reducing agent, such as polytetrafluoroethylene, into a contact portion that engages the field winding or by integrally molding such a member and the contact portion. The member used, however, has too low a friction coefficient of about 0.05, which in turn causes even greater variations in the frictional force. This is considered to occur due to the fact that the thickness of the coated friction coefficient reducing agent is not necessarily uniform.
Further, because the friction coefficient is small, the length that the field winding slips becomes large, increasing a range of frictional force variations.
As a result, when this member is incorporated into a rotor, the rotor shaft is bent to a significant extent, increasing the shaft oscillations. Further, in the example of the sliding sheet or friction-reducing member, because it has a very small thickness, when the field winding is repetitively subjected to thermal elongations and therefore frictions, the sheet is likely to be broken, and this becomes a problem in strength.
An object of the present invention is to provide a rotary electric machine which minimizes frictional force variations caused by the field winding of the rotor being thermally expanded and thereby reduces the bending of the rotor shaft even when the thermal expansion of the field winding repetitively occurs.
The object stated above can be achieved by a rotary electric machine which comprises a stator frame, a rotor mounted on the stator frame through bearings, a plurality of slots formed in an outer circumferential surface of the rotor; a field winding installed in the slots, and creepage blocks for electric insulation supported in openings of the rotor in contact with the field winding, wherein each of the creepage blocks is formed by pressing together a resin member containing reinforcement fibers and organic fibers for contact with the field winding.
Further, the above objective can also be realized by a rotary electric machine which comprises a stator frame, a rotor mounted on the stator frame through bearings, a plurality of slots formed in an outer circumferential surface of the rotor, a field winding installed in the slots, and creepage blocks for electric insulation supported in openings of the rotor in contact with the field winding, wherein each of the creepage blocks comprises prepreg sheets and organic fibers for contact with the field winding, the prepreg sheets having reinforcement fibers aligned in a direction, impregnated with semi-hardened resin and fixed together, and the organic fibers for contact with the field winding are oriented to a direction of axis of the rotor.
Further, the above objective can also be realized by a rotary electric machine wherein each of the creepage blocks comprises prepreg sheets and organic fibers for contact with the field winding, the prepreg sheets having reinforcement fibers that are aligned in a direction, impregnated with semi-hardened resin and fixed together, and the organic fibers are short and directed in random directions.
Further, the above objective can also be achieved by a rotary electric machine wherein the organic fibers for contact with the field winding include fibers made from polybenzoimidazole, polyparaphenylene benzobisoxazole, aromatic polyamide, polyarylate, and aromatic polyester.
Further, the above objective can also be realized by a rotary electric machine wherein the organic fibers for contact with the field winding include fibers with a heat resistance of 300xc2x0 C. or higher.
Further, the above objective can also be realized by a rotary electric machine wherein a surface of the organic fibers for contact with the field winding is combined with fibers made from polyethylene, polypropylene and nylon.
Further, the above objective can also be realized by a rotary electric machine wherein the surface of the organic fibers for contact with the field winding is machined so that the organic fibers are exposed at the surface.
Further, the above objective can also be realized by a rotary electric machine wherein the surface of the organic fibers for contact with the field winding has a thickness equal to or less than one fourth the thickness of the creepage block.
Further, the above objective can also be realized by a rotary electric machine wherein each of the creepage blocks is formed with holes extending in a direction of a thickness of the block and members containing organic fibers are inserted in the holes.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.